Abstract Parental autonomy support, the extent to which parents facilitate their child's independent use of decision‐making and problem‐solving skills, is an important contributor to adolescent development. This study aimed to explore the effect of parental autonomy support on academic burnout and loneliness among adolescents and whether this link was mediated by the emotion reactivity of the adolescent. Participants ( N = 965) were recruited from a Chinese middle school and completed a three‐wave longitudinal study, filling out the Parental Autonomy Support Scale, the Emotion Reactivity Scale, the School Burnout Inventory and the University of California at Los Angeles Loneliness Scale. The results revealed that T1 parental autonomy support negatively predicted T2 emotional reactivity and T3 loneliness, but it did not predict T3 academic burnout. T2 emotional reactivity negatively predicted T3 academic burnout, but it did not predict T3 loneliness. T2 emotion reactivity mediated this relationship between T1 parental autonomy support and T3 academic burnout. This is the first study to identify the mediating role of emotion reactivity between parental autonomy support and academic burnout and loneliness. It demonstrated the need for parents to pay attention to the way they support their adolescents' autonomy and help them manage their emotion reactivity.